SAN FRANCISCO (AP) — The refusal of a convicted steroids dealer to testify at Barry Bonds' perjury trial has already left the prosecution without key evidence, and the defense wants even more of it barred.

Just how much damage Greg Anderson's decision to go to prison on contempt charges rather than testify against the baseball slugger will be determined at two pivotal court hearings over the next month.

In the first hearing Friday, court filings show Bonds' attorney will seek to exclude from the March trial a massive trove of evidence prosecutors say helps prove the former San Francisco Giant knowingly took steroids as he pursued the single-season and career home run records.

U.S. District Court Judge Susan Illston has already barred prosecutors from introducing three urine tests that allegedly show Bonds using steroids in 2000 and 2001. The tests were seized during a 2003 raid of the Bay Area Laboratory Co-Operative, which was the center of a widespread sports doping ring.

The judge ruled that without Anderson testifying that he took the sample directly from Bonds' to the lab, it's impossible to prove that the test results belong to the baseball player. The 9th U.S. Circuit Court of Appeals upheld that decision in a 2-1 ruling dismissing prosecutors' appeal.

"It's a very important hearing involving key evidence," said Vermont Law School professor Michael McCann, a sports law expert. "Bonds goes into this with the score ahead."

Bonds, 46, has pleaded not guilty to 10 counts of perjury and one charge of obstruction for testimony in December 2003 before a grand jury investigating sports doping. Bonds testified that that he never knowingly took performance enhancing drugs and that no one other than his doctor ever injected him with any substances.

Prosecutors allege that Bonds knew those statements were false and that his testimony was "material" to the grand jury, meaning the slugger's testimony somehow affected or altered the sports doping investigation.

On Friday, Bonds' attorneys will urge Illston to toss out even more evidence directly tied to Anderson.

They are also trying to bar the testimony of several former teammates and current player Jason Giambi, most of whom Anderson identified as his steroids customers during a government raid on his apartment on the same day as the raid on the lab in September 2003.

The prosecutors oppose Bonds' attempt to exclude just about everything and everyone connected with Anderson. They are also asking the judge to reconsider her ruling excluding so-called doping calendars with the initials "BB" and "BLB" and handwritten notes labeled "Barry." These were documents seized during the raid of Anderson's house that prosecutor say show a detailed drug regimen Anderson administered to Bonds.

Anderson, who served three months in prison after pleading guilty in 2005 to steroids distribution and money laundering, refused to answer questions about Bonds during the raid and afterward. Anderson spent a little more than a year in prison on contempt charges for refusing to testify before the grand jury investigating Bonds for perjury.

Nevertheless, prosecutors allege lead investigator Jeff Novitzky and several other agents seized numerous documents detailing an illicit relationship between Bonds and Anderson.

"The documents from Anderson's residence provide a detailed record of steroid distribution from Anderson to Bonds from 2001 to 2003," prosecutors said in a court filing earlier this month, "with entries referring to injectable steroids, human growth hormone and other drugs."

However, the judge in her initial 2009 order also excluded most of those documents seized at Anderson's house without the trainer's testimony.

But on Friday, the prosecutors will renew their fight for admitting those documents by arguing they show Bonds' allegedly false testimony affected the grand jury's sports doping investigation because the statements "were completely inconsistent with voluminous documents" showing BALCO executives and Anderson "distributing drugs to Bonds and monitoring his use of those drugs."

The prosecutors said they need the Anderson documents to put Bonds' testimony in context.

Prosecutors proposed editing out any mention of positive drug tests in the documents.

Bonds lawyers reply that the prosecutors' arguments "mock" the judge's previous order barring the evidence. They urge the judge to "reaffirm" her previous order.